I am upgrading the rear turn signals on my BMW and my wife's Volvo, since they use the same bulb. Now, neither of us like the seizure inducing double-blink rate, so resistors are the way to go. Since there is little space in the rear to put the resistor, I am wondering about placement.

For the front turn signal resistors, the resistor can heat to 300 degrees. Is this true for the rear turns signals, which are not continuously on?

I have seen one person use 3M tape to mount the rear resistor, is this correct if it heats to 300 degrees?

The resistors will heat up so I don't recommend mounting them by the metal surface. I recommend securing them by the wires or with screws that can withstand that kind of temperature. Also make sure to mount them on an unpainted surface, away from any plastic or areas that can melt.